JPS6226603B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse train detection method for detecting the number of pulse trains and their pulse repetition intervals from incoming pulses in which a plurality of pulse trains coexist.

This type of conventional detection method selects two pulses from among the arriving pulses, considers them to be two adjacent pulses of a certain pulse train, extrapolates the pulse train, and determines whether there is a match among the arriving pulses. It was based on a process of trial and error, in which the user had to judge whether the pulse was available or not, and if it was not available, select another two pulses and repeat the same process.

FIG. 1 shows an example of detection using this conventional method.
In the figure, a represents an incoming pulse in which five pulse trains with different repetition intervals are superimposed. In this column, the two pulses to be selected are sequentially selected: the first and second pulses, the first and third pulses, the first and fourth pulses, and so on. First, if you select the first and second pulses and extrapolate them, you will get something like b, but since there is nothing in a that matches these, proceed to the next step and select the first and second pulses like C. Extrapolation is performed on the third pulse. The process continues in the same manner, and only when f is reached can one pulse train included in a be found. Next, exclude the pulses belonging to the found pulse train and find another pulse train using the same procedure as before. The first step is shown in g. By repeating this process, all pulse trains included in the arriving pulses are detected.

Since the conventional detection method is configured as described above, it is necessary to continue trial and error in selecting two pulses until two adjacent pulses in the pulse train are encountered. The drawback was that if there were omissions, it would take an unnecessarily long time.

This invention was made to eliminate the drawbacks of the conventional detection method as described above, and by classifying pulse intervals and adding certain processing, the number of pulse trains included in an incoming pulse and the number of pulses contained in those pulses can be determined. The purpose is to provide a method that can detect repetition intervals all at once.

An embodiment of the present invention will be described below with reference to the drawings.

Here, since the present invention identifies PRI using a function using an autocorrelation function, the basic principle will be explained first.

Let the arrival times of the pulse train be t ₁ , t ₂ , ..., t _N , and the sum of the impulses of the pulse train is: The autocorrelation function c of this pulse train is expressed as
(τ) is becomes. Then, by taking this c(τ) on the vertical axis and τ on the horizontal axis, and subdividing the τ axis and integrating over each subdivision section, the height corresponding to the number of pulses is placed at the position corresponding to the PRI of each single pulse train. A peak appears, which allows estimation of each PRI. However, with this method, peaks of approximately the same height are also created at positions that are integral multiples of PRI, so this
In order to suppress peaks that occur at positions that are integral multiples of PRI, ie, "fractional harmonics," the present invention further performs a transformation defined by the following equation on the pulse trains g and t.

This is obtained by multiplying each term on the right side of the above autocorrelation function by the phase factor exp[-2πitn/(tn-tm)], and this factor almost completely eliminates the fractional harmonics appearing in the autocorrelation function. It also works to suppress levels other than the peak, and as a result, only the PRI is extracted as a peak.

Examples based on this basic principle will be described below with reference to the drawings. In Figure 2, input terminal 1
From the measurement data t ₁ of the arrival time of the incoming pulse,
t ₂ , ..., t _N are input. Here, we only consider the arrival time as a pulse parameter, so
From now on, the pulse and the arrival time will be treated as the same. These input signals are first applied to pulse repetition interval (pRI) filters 2 ₁ , 2 ₂ , ..., 2 _K , each of which has a
The subdivisions [τ _k-1 , τ _k ) of the PRI axis as shown in (however, the interval [τ _k-1 , τ _k ) represents τ _k-1 τ<τ _k ] correspond, and the third As shown in Figure b, for pulse t _n , prior to it t _n −τ _k <t
The pulse t _n is passed only when the pulse exists in the interval expressed by t _n -τ _k-1 . Also, t _n −
The difference t _n -t _o from the pulse t _n existing at τ _k <tt _n -τ _k-1 is also output at the same time. Therefore, the function of the PRI filters 2 ₁ , 2 ₂ , ..., 2 _K is the pulse interval t _n -t _o , (m=2, 3, ..., N, n=m-1,
m-2, ..., 1) is divided into preset PRI subdivision intervals [τ ₀ , τ ₁ ), [τ ₁ , τ
₂ ), ..., [τ _k-1 , τ _k )]. PRI filter 2 ₁ , 2
The signal that has passed through ₂ ,..., _2K is sent to the divider circuit ₃₁ ,
The division t _n /(t _n -t _o ) is performed by 3 ₂ ,..., 3 _K , and then the complex trigonometric function calculation circuit 4 ₁ ,
4 ₂ ,..., 4 _K , exp[2πit _n /(t _n -t _o )] is calculated, and finally the accumulation circuits 5 ₁ , 5 ₂ ,
..., _5K addition will be held. The number of pulse trains and their PRI are the absolute values of the outputs of the accumulator circuits 5 ₁ , 5 ₂ , ..., 5 _K |D _K
It is detected by comparing |.

Next, the operation of this detection method will be explained.
Now, in the arriving pulse as shown in Figure 4a,
Assume that pulse trains t _o1 , t _o2 , . . . , t _op are included, as shown in FIG. r is K among the subdivisions of the PRI axis
i.e., τ _k-
1 If r<τ _k , the output from the accumulator circuit 5 _k is It should contain. In addition to this, the output from the accumulator circuit 5 _k happens to have a pulse interval of τ _k-
1 t _n −t _o <τ _k , so there is a possibility that something gets mixed in. However, due to the complex trigonometric function calculation circuit 4 _k , its argument varies and its contribution to the output of the accumulator circuit 5 _k is few. Therefore, the output of the accumulator circuit 5 _k is almost equal to (2), and its absolute value is |D _K |=P-1. A pulse train with PRI equal to r also has PRI
It can also be seen as a superposition of pulse trains where is equal to kr (k = 2, 3, ...), but in this case, since the argument of the complex trigonometric function is distributed at equal intervals of 2π/k, The outputs of the accumulator circuit 5 _k cancel each other out and take a value close to 0. On the other hand, if there is no pulse train corresponding to the subdivision interval [τ _k-1 , τ _k ) of the PRI axis, there will be two problems: fewer pulses will pass through the PRI filter, and the argument angles of multiple trigonometric functions will vary. For this reason, the output from the accumulator circuit _5k also takes a value close to zero. Therefore, if the output from the accumulator circuit 5 _k takes a large value, it can be determined that this is because a pulse train whose PRI belongs to [τ _k-1 , τ _k ) exists. FIG. 5 shows an example of detection by this embodiment.
In the figure, a is the same as a in FIG. 1, and is an incoming pulse in which five pulse trains with different PRIs are superimposed. A diagram b is a diagram drawn by taking the absolute values of the outputs of the accumulator circuits 5 ₁ , 5 ₂ , . . . , 5 _k in the embodiment shown in FIG. 2 for this arriving pulse. As can be seen from the graph b, there are five pulse trains and their PRI values can be detected.

Note that in the above embodiment, the division circuits 3 ₁ , 3 ₂ ,
..., _3k shows a method that performs division t _n /(t _n -t _o ), but instead, division t _o /(t _n -t
_o ), or division 2t _n / (τ _k-1 + τ _k ) or 2t _o /
Even if (τ _k-1 +τ _k ) is performed, almost the same value is obtained, so the same effect is expected.

As described above, according to the present invention, the detection method is configured such that the number of pulse trains and their PRIs can be detected by comparing the absolute values of the sums of complex trigonometric functions, so that multiple PRIs can be detected simultaneously. This has the effect of being able to detect noise pulses or missing pulses in a relatively short time.

[Brief explanation of the drawing]

Figures 1a to 1g are diagrams showing detection examples using conventional detection methods, Figure 2 is a block diagram of an embodiment of the present invention, Figure 3 is a diagram for explaining this embodiment, and Figure 4 is a diagram showing an example of detection using a conventional detection method. Figure 5 for explaining the operation of this invention
The figure shows an example of detection according to this embodiment. 1: Input terminal, 2 ₁ , 2 ₂ ,..., 2 _K : PRI filter, 3 ₁ , 3 ₂ ,..., 3 _K : Division circuit, 4
₁ , 4 ₂ ,..., 4 _K : Complex trigonometric function calculation circuit, 5
₁ , 5 ₂ ,..., 5 _K : Accumulator circuit.

Claims (1)

[Claims] 1. From the measurement data of the arrival times t ₁ , t ₂ , ... t _N of arriving pulses in which a plurality of pulse trains are mixed, the pulse interval t _n -t _o (where m = 2, 3, ..., N , n=1,
2,..., m-1), and these are subdivided intervals of the preset pulse repetition interval [τ ₀ , τ ₁ ), [τ ₁ , τ ₂ ),..., [τ _k-
1 , τ _k ) ([τ _k-1 , τ _k ) is the interval τ _k-1 ≦τ
<τ _k ), and calculate the value of the addition formula of the complex trigonometric function in equation (1) below for the data in each of these subdivision intervals, and each subdivision obtained by this A pulse train detection method characterized by outputting the number of the plurality of pulse trains and the pulse repetition interval of each pulse train from the absolute value of the interval. However, θ is 2πt _n /(t _n −t _o ), 2πt _o /
(t _n −t _o ), 4πt _n /(τ _k-1 +τ _k ), or 4π
It is either t _o /(τ _k-1 + τ _k ).